Chain drive, especially a camshaft/camshaft drive for a motor vehicle

ABSTRACT

The present invention relates to a chain drive, in particular camshaft/camshaft drive for an automotive engine, the chain drive comprising at least two chain gears and a drive chain. Such a chain drive shall be made more compact without excessively great losses in its low-noise characteristics. To this end at least two chain gears are arranged in laterally offset relationship with one another in axial direction. The drive chain is a multiple-track chain. Each of the offset chain gears has assigned thereto a separate track of the multiple-track chain due to the lateral offset. The tip diameters of the offset chain gears are overlapping.

[0001] The present invention relates to a chain drive, in particularcamshaft/camshaft drive for an automotive engine, the chain drivecomprising at least two chain gears and a drive chain.

[0002] In particular in the field of internal combustion engines, thereis a need for reliably functioning control chain drives. In this respecthigh demands are made on the low-noise characteristics of such chaindrives, so that numerous measures are taken for preventing unnecessaryvibrations as well as running noise caused thereby. It is generallyknown that a quiet run can be expected when the number of teeth of thechain gears is great; that is why small chain gear sizes are notwillingly accepted. On the other hand, more and more efforts are made toprovide compact internal combustion engines as well as chain drivesneeded therefor. In a camshaft/camshaft drive for an automotive engine,limits are already set by the axial distance between the two camshafts,which must be kept in mind.

[0003] It is therefore the object of the present invention to improve achain drive of the above-mentioned type with respect to its compactness,with noise or wear aspects being paid attention to.

[0004] According to the invention this object is achieved in that atleast two chain gears are arranged in laterally offset relationship withone another in axial direction, the drive chain is a multiple-trackchain, each of the offset chain gears has assigned thereto a separatetrack of the multiple-track chain due to the lateral offset, and the tipdiameters of the offset toothed wheels are overlapping. Normally,multiple-track chains are only used in fields where they are inengagement with a multiple-track chain gear to be able to transmit largeforces. In this case, however, a multiple-track chain is used forsimultaneously driving chain gears that are laterally offset to oneanother, namely in the form that the chain gears are even overlapping.With a standard arrangement without a lateral offset, such an overlapwould of course not be possible. At the same time, however, the numberof teeth of the chain gears can be kept large despite the axial distancewhich is per se too small so as to achieve a run of the multiple-trackchain that is as quiet as possible. Theoretically, it would be possiblewith such an arrangement to make the chain gears overlapping to such anextent that the gearing of the one chain gear almost contacts the axisof the other chain gear. When a projection of the axes is avoided, aneven greater overlap would be possible. However, the two chain gearsshould not be seated on a joint axle or shaft, but should drivedifferent elements (e.g. camshafts). The number of the offset chaingears can be chosen in dependence upon the number of the tracks of themultiple-track chain. The chain gears can have different tooth numbers.

[0005] In dependence upon the speeds to be used and the forces to betransmitted, it may further be necessary for the prevention of tiltingmoments that at the side next to the gearings of the overlapping chaingears a respective support means is provided for the track of themultiple-track chain that is not in engagement with the associated chaingear. The force of the chain gear acting on the multiple-track chain isasymmetrical relative to the longitudinal center line of themultiple-track chain, so that corresponding asymmetrical forces areacting thereon. Support means help to prevent a lateral tilting of themultiple-track chain, whereby noise can once again be minimized becausecorresponding vibrations are suppressed.

[0006] Track means each time that part of the multiple-track chain thatis laterally provided next to a chain gear but not in engagementtherewith. Said track is of course in engagement with the respectivelyother chain gear.

[0007] In case the track is to be supported by the chain gearsthemselves, such a configuration has its limits. It is thereforepreferred in one embodiment that an overlap of the chain gears isgreater than the sum of the height of the plates of the multiple-trackchain and of the difference of tip circle radius less pitch circleradius. A support means integrated on the chain gear would come intocontact with the gearing of the respectively other chain gear in thecase of such a dimensioning rule.

[0008] According to a further embodiment it is therefore intended toprovide slide rails as support means. As a rule, these are at astandstill relative to the chain gears, and the track is slidingtherealong. Slide rails have already been used in chain drives for verydifferent purposes for a long time so that the problems associatedtherewith have already been solved in the prior art in many ways.Materials and, if necessary, also lubricant supply can readily be usedfor the slide rails. It is also possible to choose a multipartconstruction of the slide rails. Known is e.g. the use of a relativelystable basic body and a slide lining which is arranged thereon and canbe removed and exchanged in part.

[0009] Preferably, a distance of the slide surface of the slide rail maysubstantially be equal to half the plate height or half a roller heightat least in the area of the wrap angle of the multiple chain on theassociated chain gear to the pitch circle of the chain gear. It is hereof importance whether the plates are to be supported by the supportmeans or whether the rollers of a multiple-track chain are to be usedfor the support. The dimensioning rule ensures that the hinge axes ofthe multiple-track chains are oriented as parallel as possible relativeto the axes of the chain gears.

[0010] According to a further variant a great advantage is that theslide rail comprises a transfer extension which supports the track ofthe multiple-track chain in the section between the overlapping chaingears. Despite the overlapping chain gears a section remains in mostcases between the two wheels where the multiple-track chain is neitherin engagement with the one nor the other chain gear. To avoid excessivevibrations and associated noise upon exit from the one chain gear and/orentry on the other chain gear, a support is also provided for this area.

[0011] Advantageously, the transfer extensions of the slide railsassigned to the overlapping chain gears can overlap and jointly supportthe multiple-track chain in the section between the overlapping chaingears. When both slide rails are equipped with such transfer extensions,a tilting movement of the multiple-track chain is also avoided in theintermediate part between the chain gears because the multiple-trackchain is supported over its whole width.

[0012] A smooth entry or exit of the multiple-track chain is ensuredwhen according to one embodiment a slide surface of the transferextension passes tangentially into the adjoining remaining slide surfaceof the slide rail.

[0013] To give the slide rail a sufficiently stable configuration and tomake the transfer extension as rigid as possible, a bottom side of theslide rail which defines at least the transfer extension is arcuatelyadapted to the outer contour of the other chain gear. In a particularembodiment this has even the effect that the multiple-track chain iscompletely supported between the exit point on the first chain gear andthe exit point from the second one of the overlapping chain gears. Thetransfer extensions are guided relatively close to the other chain gear,resulting each time in only small portions on which the track is notsupported. However, the multiple-track chain is respectively supportedin said portions by the transfer extensions arranged in offsetconfiguration relative thereto. The bottom side of the transferextension is each time adapted relatively close to the outer contour ofthe adjoining chain gear, so that a stable support of the slide surfacecan be realized without a design that is too filigree.

[0014] Furthermore, it is of advantage when the chain gears have thesame size and tooth number. It is here in particular possible to givealso the slide rails an identical design and to arrange each in offsetrelationship with respect to one another.

[0015] An embodiment of the present invention shall now be explained inmore detail with reference to a drawing, in which:

[0016]FIG. 1 is a schematic front view on the upper part of acamshaft/camshaft chain drive; and

[0017]FIG. 2 is a schematic top view on the chain drive of FIG. 1,wherein the slide chains have been omitted for the sake of clarity.

[0018]FIG. 1 shows the upper part of a camshaft/camshaft drive. Thefirst chain gear 1 is seated on a first camshaft 2, and the second chaingear 3 is seated on a second camshaft 4. Chain gears 1, 3 are connectedto camshafts 2, 4 by means of standard connection methods. Thearrangement of the chain drive in a chain case or a closed enginechannel shall not be discussed in more detail in the following.

[0019] In the present embodiment, each of chain gears 1, 3 has 40 teeth.The pitch is 9.525 mm.

[0020] The two chain gears 1, 3 have guided therearound a duplex chain 5which is also in engagement with a gear (not shown) of the crankshaft.The duplex chain is constituted by two plate type roller chains of astandard construction which are arranged in parallel with one anotherand interconnected by means of an intermediate pin plate. Such duplexchains 5 are also called double roller chains.

[0021] The axial distance A of the two chain gear axes has been chosensuch that the two chain gears 1, 3 are overlapping. However, as can beseen in FIG. 2, these are arranged to be laterally offset relative toone another when viewed in axial direction, so that they are arrangedside by side in their overlap area 6. In the present embodiment, thechain gear 1 is positioned behind the chain gear 3 (starting from FIG.1). The center distance M of the two chain gears 1 and 3 relative to oneanother also corresponds to the associated center distance M of theduplex chain 5 and is 10.34 mm in the present embodiment. This centerdistance M could also be referred to as the offset of the two chaingears 1, 3. Thus the chain gear 1 is in engagement with a first track 7and the chain gear 3 with a second track 8 of the duplex chain 5. Sinceeach of said chain gears 1, 3 has assigned thereto a track 7, 8 of itsown, it is possible to provide an overlap area 6. FIG. 2 shows theoverlap T of the pitch circles T_(D) of the two chain gears 1, 3. Inthis embodiment T is equal to 10 mm. However, the tip diameters d_(K) ofthe two chain gears 1, 3 must also be taken into account for a support,which will still have to be described in more detail in the following.

[0022] A slide rail 9 and 10, respectively, is positioned laterally nextto a chain gear 1 or 3.

[0023] If it is assumed in the present example that the runningdirection of chain L is clockwise, the wrap angle α of the duplex chainis 90° in the first chain gear 1 between entry point 11 and exit point12. This is also true for the second chain gear 3 in the case of which awrap angle α of 90° is formed between entry point 13 and exit point 14.In this area, the slide rails 9, 10 have an arcuate slide surface 15 and16, respectively. The distance of the slide surfaces 15, 16 relative tothe associated pitch circle T_(D) of the chain gears 1 or 3 is hereequal to half the height H of a plate 17 of the duplex chain 5. However,it is also possible to adapt the slide rails 9, 10 with their slidesurface 15 and 16, respectively, to the rollers 18 of the duplex chain5, so that these roll on the slide surface 15 or 16. The pitch circleT_(D) is drawn in FIG. 1 in each chain gear 1 and 3.

[0024] The slide rails 9, 10 are secured to a stationary part, e.g. theengine casing, or are mounted on a bearing seat section and are at astandstill relative to the chain gears 1, 3. In the intermediate part19, which is essentially of length A, the duplex chain 5 is no longersupported by the chain gear 1 or 3. To avoid unnecessary vibrations inthis area 19, each of the slide rails 9, 10 has a transfer extension 20and 21, respectively. The transfer extension 20, 21 has the shape of anose or a triangle, the slide surface of the transfer extension 20, 21passing tangentially into the remaining slide surface 15 and 16,respectively, of the slide rails 9, 10. The slide surface of thetransfer extension 20, 21 extends substantially along a straight line.As can be seen in FIG. 1, the two transfer extensions 20, 21 areoverlapping, so that both tracks 7, 8 of the duplex chain 5 aresupported in the area of the intermediate part 19.

[0025] Each of the two slide rails 8, 10 ensures that no tilting momentsare acting on the duplex chain 5 and that, as a consequence, excessivevibrations will not arise, in particular, upon entry on a chain gear orexit from a chain gear. The slide rails 9, 10 may e.g. consist of awear-resistant plastic material. However, it is also possible to producethe rails from a basic body of e.g. aluminum and to provide them with aslide lining which is possibly removable. The bottom side 22, 23 of theslide rails 9, 10 which defines the transfer extension 20, 21 is adaptedto the outer contour of the adjoining chain gear 1 or 3 and arranged ata small distance from said wheel. It is thereby also possible to givethe transfer extension 20, 21 a very stable design. Each of the sliderails 9, 10 is drawn down to the level of the entry point 11 and exitpoint 14, respectively, and has a substantially arcuate form with thetransfer extension 20, 21 arranged at one side. A truss structureincreases the stability at a low weight.

[0026] Thanks to the use of the slide rails 9, 10, it is possible toproduce relatively large overlap areas 6 because the boundary of theoverlaps just depends on the size of the camshafts 2, 4.

[0027] Except for the specifically molded-on slide rails 9 and 10, onlystandard machine elements are used in the present construction so thatit is possible to create the arrangement according to the invention bymaking a few modifications.

1. A chain drive, in particular camshaft/camshaft drive for anautomotive engine, comprising at least two chain gears (1, 3) and adrive chain (5), characterized in that at least two chain gears (1, 3)are arranged in laterally offset relationship with one another in axialdirection, said drive chain (5) is a multiple-track chain, each of saidoffset chain gears (1, 3) has assigned thereto a separate track (7, 8)of said multiple-track chain (5) due to the lateral offset, and the tipdiameters (d_(K)) of said offset chain gears (1, 3) are overlapping. 2.The chain drive according to claim 1, characterized in that at the sidenext to the gearings of the overlapping chain gears (1, 3) a supportmeans (9, 10) is respectively provided for the track of saidmultiple-track chain (5) which is not in engagement with the associatedchain gear (1, 3).
 3. The chain drive according to claim 1 or 2,characterized in that an overlap (d_(K)-A) of said chain gears (1, 3) isgreater than the sum of the height (H) of the plates (17) of saidmultiple-track chain (5) and of the difference of tip circle radius(d_(K)/2) less pitch circle radius (d_(D)/2).
 4. The chain driveaccording to any one of claims 2 or 3, characterized in that slide rails(9, 10) are provided as support means.
 5. The chain drive according toclaim 4, characterized in that a distance of the slide surface (15, 16)of said slide rail (9, 10) substantially corresponds to half the plateheight (H/2) or half the roller height at least in the area of the wrapangle (α) of said multiple-track chain (5) on the associated chain gear(1, 3) relative to the pitch circle (T_(D)) of said chain gear (1, 3).6. The chain drive according to any one of claims 1 to 5, characterizedin that said slide rails (9, 10) have a transfer extension (20, 21)which supports the track (7, 8) of said multiple-track chain (5) in thesection (19) between said overlapping chain gears (1, 3).
 7. The chaindrive according to claim 6, characterized in that said transferextension (20, 21) of said slide rails (9, 10) assigned to saidoverlapping chain gears (1, 3) are overlapping and jointly support saidmultiple-track chain (5) in said section (19) between said overlappingchain gears (1, 3).
 8. The chain drive according to claim 6 or 7,characterized in that a slide surface of said transfer extension (20,21) passes tangentially into the adjoining remaining slide surface (15,16) of said slide rail (8, 9).
 9. The chain drive according to any oneof claims 6 to 8, characterized in that a bottom side (22, 23) of saidslide rail (9, 10) which defines at least said transfer extension (20,21) is arcuately adapted to the outer contour of said other chain gear(1, 3).
 10. The chain drive according to claims 1 to 9, characterized inthat said multiple-track chain (5) is completely supported between anentry point (11) on said first chain gear (1) and an exit point (14)from said second chain gear (3).
 11. The chain drive according to anyone of claims 1 to 10, characterized in that said chain gears (1, 3)have the same size and tooth number.